Research Article West Africa Extreme Rainfall Events and Large-Scale Ocean Surface and Atmospheric Conditions in the Tropical Atlantic S. Ta, 1 K. Y. Kouadio, 1 K. E. Ali, 1,2 E. Toualy, 1 A. Aman, 1 and F. Yoroba 1 1 Laboratory of Atmospheric Physics and Fluid Mechanics, University FHB of Cocody-Abidjan, 22 BP 582, Abidjan 22, Cˆ ote d’Ivoire 2 Institut National Polytechnique F´ elix Houphou¨ et Boigny de Yamoussoukro, BP 1093, Yamoussoukro, Cˆ ote d’Ivoire Correspondence should be addressed to S. Ta; biladjisamuelta@outlook.com Received 6 April 2016; Revised 11 June 2016; Accepted 26 June 2016 Academic Editor: Anthony R. Lupo Copyright © 2016 S. Ta et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Based on daily precipitation from the Global Precipitation Climatology Project (GPCP) data during April–October of the 1997– 2014 period, the daily extreme rainfall trends and variability over West Africa are characterized using 90th-percentile threshold at each grid point. Te contribution of the extreme rainfall amount reaches ∼50–90% in the northern region while it is ∼30– 50% in the south. Te yearly cumulated extreme rainfall amount indicates signifcant and negative trends in the 6 ∘ N–12 ∘ N; 6 ∘ N– 12 ∘ N; 17 ∘ W–10 ∘ W and 4 ∘ N–7 ∘ N; 4 ∘ N–7 ∘ N; 6 ∘ E–10 ∘ E4 ∘ N–7 ∘ N; 6 ∘ E–10 ∘ E4 ∘ N–7 ∘ N; 6 ∘ E–10 ∘ E domains, while the number of days exhibits nonsignifcant trends over West Africa. Te empirical orthogonal functions performed on the standardized anomalies show four variability modes that include all West Africa with a focus on the Sahelian region, the eastern region including the south of Nigeria, the western part including Guinea, Sierra Leone, Liberia, and Guinea-Bissau, and fnally a small region at the coast of Ghana and Togo. Tese four modes are infuenced diferently by the large-scale ocean surface and atmospheric conditions in the tropical Atlantic. Te results are applicable in planning the risks associated with these climate hazards, particularly on water resource management and civil defense. 1. Introduction Rainfall is one of the most usable weather parameters that allows determining climate variability, particularly in West Africa [1, 2]. Its quantifcation is a great concern in the tropics as it plays a signifcant role in hydrological and climate studies. Furthermore, the social and economic development of West Africa countries is strongly linked to agricultural and water resources [3]. In the last several decades, alteration of periods with extreme rainfall events with dry conditions has led to a succession of food/drought years [4]. Tese extreme events constitute the primary impact of the climate change on society [5] since their frequencies have more impact compared to changes in mean climate [6]. Te spatiotemporal distribution of the extreme rainfall events is not homogenous in West Africa. Tey can cause fooding or drought that have negative impacts by increasing environmental disasters. For example, rainfall irregularity leads to disastrous consequences if a drought situation persists. Tat was the case in the early 1970s during which the Sahel region experienced severe drought and devastating famine [7]. On the other hand, food periods can have dramatic consequences in poor countries of West Africa. Such situation was observed in 1994 when the runof of the Bagr´ e Dam in Burkina Faso reached 2050 m 3 s −1 instead of the initial project runof of 1520 m 3 s −1 [8]. Another fooding episode (>300 mm of rainfall amount) occurred during August 31 to September 01, 2009, in Ouagadougou (Burkina Faso) where it caused serious damage due to the overfowing of drainage channels and the dam. Consequently trafc was disrupted, houses were destroyed, and patients from Yalgado Ou´ edraogo Hospital were evacuated (http://reliefweb.int/ disaster/f-2009-000172-bfa). Te southern region of West Africa also has experienced social and economic impacts due to fooding, as, for instance, the episodes that caused many deaths in Abidjan (Cˆ ote d’Ivoire, 39 deaths in 2014 and 16 deaths on June 22, 2015; see http://www.rf.fr/afrique/ 20150621-cote-ivoire-bilan-victimes-intemperies-pluies-abidjan). Hindawi Publishing Corporation Advances in Meteorology Volume 2016, Article ID 1940456, 14 pages http://dx.doi.org/10.1155/2016/1940456